New observations and simulations show that jets of high-speed particles emitted by supermassive black holes can be used to map the structure of invisible inter-cluster magnetic fields. These findings provide astronomers with a new tool for investigating previously unexplored aspects of clusters of galaxies. Publication in Nature on May 5th.
Clusters of galaxies grow through collisions with surrounding matter, which create bow shocks in the dilute plasma. The plasma motion induced by these activities can drape intra-cluster magnetic layers, forming virtual walls of magnetic force. These magnetic layers, however, can only be observed indirectly when something interacts with them. Because it is difficult to identify such interactions, the nature of intra-cluster magnetic fields remains poorly understood. A new approach to map and characterize magnetic layers is highly desired.
unusual jet structures
An international team of astronomers, including Hiroki Akamatsu (SRON Netherlands Institute for Space Research), used the MeerKAT radio telescope located in South Africa to observe a bright galaxy in the merging galaxy cluster Abell 3376 known as MRC 0600-399. Located more than 600 million light-years away in the direction of the constellation Columba, MRC 0600-399 is known to have unusual jet structures bent to 90-degree angles. Previous X-ray observations revealed that MRC 0600-399 is the core of a sub-cluster penetrating the main cluster of galaxies, indicating the presence of strong magnetic layers at the boundary between the main and sub-clusters. These features make MRC 0600-399 an ideal laboratory to investigate interactions between jets and strong magnetic layers.
double-scythe
The MeerKAT observations revealed unprecedented details of the jets, most strikingly, faint “double-scythe” structure extending in the opposite direction from the bend points and creating a “T” shape. These new details show that, like a stream of water hitting a pane of glass, this is a very chaotic collision. Dedicated computer simulations are required to explain the observed jet morphology and possible magnetic field configurations.
supercomputer
The team performed simulations on NAOJ’s supercomputer ATERUI II, the most powerful computer in the world dedicated to astronomical calculations. The simulations assumed an arch-like strong magnetic field, neglecting messy details like turbulence and the motion of the galaxy. This simple model provides a good match to the observations, indicating that the magnetic pattern used in the simulation reflects the actual magnetic field intensity and structure around MRC 0600-399. More importantly, it demonstrates that the simulations can successfully represent the underlying physics so that they can be used on other objects to characterize more complex magnetic field structures in clusters of galaxies. This provides astronomers with a new way to understand the magnetized Universe and a tool to analyze the higher-quality data from future radio observatories like the SKA (the Square Kilometre Array).